Generally, shift gear sets are provided to a synchromesh-type manual transmission apparatus in order to configure four to seven forward shift stages. Each of the shift gear sets is selectively engaged by means of a synchromesh mechanism. An operating device for performing a shift operation of the manual transmission apparatus includes fork shafts, each of which operates the corresponding synchromesh mechanism, a shift-and-select shaft for selecting and driving one of the fork shafts, a gear lever, which is operated by a driver, and an operation force transmitting mechanism for transmitting an operation force applied to the gear lever to the shift-and-select shaft. Generally, the shift-and-select shaft is configured so as to rotate in a circumferential direction and so as to move in an axial direction thereof. In a case where the shift-and-select shaft rotates in the circumferential direction thereof in order to select one of the fork shafts (a select operation), the shift-and-select shaft moves in the axial direction thereof in order to move the selected fork shaft in an axial direction thereof (a shift operation). On the other hand, in a case where the shift-and-select shaft moves in the axial direction thereof in order to select one of the fork shafts (a select operation), the shift-and-select shaft rotates in the circumferential direction thereof in order to move the selected fork shaft in an axial direction thereof (a shift operation). In the synchromesh mechanism, which corresponds to the selected fork shaft (a selected gear stage), when a sleeve of the selected synchromesh mechanism is shift-operated by the selected fork shaft, the synchronizer ring (an input side portion) and the selected gear (an output side portion) are frictionally engaged by an inner slide mechanism of the synchromesh mechanism, thereby synchronizing a rotation of the selected gear and a rotation of an output side shaft of the manual transmission apparatus. Accordingly, the sleeve and the selected gear are fittedly connected by an engaging mechanism of the synchromesh mechanism via the synchronizer ring and the selected shift stage is established. The operation force necessary in a process of the shift operation of the synchromesh mechanism is not constant. Furthermore, a reaction force may be generated when the synchronizer ring is frictionally engaged with the selected gear or when the synchronizer ring is fittedly connected with the selected gear, and such reaction force may be transmitted to the gear lever.
A demand for improving a shift feeling when performing the shift operation by controlling changes in the operation force or the reaction force of the synchromesh mechanism is increased. A shift device of a manual transmission apparatus for a vehicle, which is disclosed in JP2003-106449A, attempts to improve the shift feeling by using inertial action, which is generated when pivoting an outer lever, which pivots around a shift-and-select shaft and to which an inertia lever and an inertia mass are provided. Furthermore, according to a shift mechanism for a manual transmission apparatus, which is disclosed in JP2008-32158A, an inertia mass is configured so as to be relatively displaced on an inertia lever, which pivots around a shift-and-select shaft, so that an inertia generated when a shift operation is performed by a driver is increased and the inertia when the shift operation is not performed by the driver is decreased, in order to decrease vibration transmitted to a gear lever.
Further, in order to enhance inertial action when a shift-and-select shaft is moved in an axial direction, an inertia mass is attached and fixed at the shift-and-select shaft itself.
However, the shift device disclosed in JP2003-106449A and the shift mechanism disclosed in JP2008-32158A are adaptable to an operating device for a manual transmission apparatus, which is configured to shift-operate a fork shaft by rotating the shift-and-select shaft in a circumferential direction thereof. Therefore, the shift device disclosed in JP2003-106449A and the shift mechanism disclosed in JP2008-32158A are not adaptable to an operating device for a manual transmission apparatus, which is configured to shift-operate the fork shaft by moving the shift-and-select shaft in an axial direction thereof.
Further, in the configuration, in which the inertia mass is attached and fixed at the shift-and-select shaft itself, a mass of sufficient weight is not easily provided because an inside space of a manual transmission apparatus is not enough to accommodate the mass. Furthermore, the inertia mass acts in accordance with both a rotation of the shift-and-select shaft in a circumferential direction thereof and a movement the shift-and-select shaft in the axial direction thereof. Therefore, a select feeling at the time of select operation, in which the appropriate fork shaft is selected, may be deteriorated.
A need thus exists to provide an operating device for a manual transmission apparatus which is not susceptible to the drawback mentioned above.